There has recently been a great deal of interest in harnessing, for useful purposes, some of the mechanical or kinetic energy in the environment that is a by-product of natural or artificial processes. Such energy includes, for example, the vibrations in machines, buildings, bridges, aircrafts, cars, and the human body and the motions of ocean waves. Depending on the nature of the source, their mechanical power spectra range from a few Hz to more than hundreds of kHz. Useful purposes that have been proposed include powering of sensors, as well as providing power for illumination and signal transmission.
Devices that capture mechanical energy from the environment and convert it to useful form are often referred to as “energy harvesters.” In some energy harvesters known from the work of others, resiliently supported mass elements oscillate when they are driven by external vibrations and the like, and in turn, the oscillating elements drive transducers that convert the kinetic energy of the oscillating elements to electrical energy.
The effectiveness of such energy harvesters is reduced by various inefficiencies related, for example, to the mechanical coupling between the external energy source and the internal mass elements, and between the internal mass elements and the transducers. As a consequence, there remains a need for improvements in conversion efficiency.